This disclosure is an interlock system directed to a multivalve manifold connecting process pressures to an instrument. A multivalve manifold is defined as three valves, typically plug or ball valves, located in common manifold body. Such multivalve manifolds are ordinarily used with differential pressure measuring instruments on pipelines. For instance, a pipeline might incorporate an orifice plate forming a restrictive pressure drop in the pipeline. Flow rate through the pipeline is derived from a measure of the pressure drop across the orifice plate. To this end, a multivalve manifold must be connected across the orifice and also to the measuring instrument. The differential pressure measuring device normally requires several interconnected valves. This apparatus discloses a multivalve manifold suitable for differential pressure type flow measuring instruments on a pipeline. It provides the valving necessary to connect a differential pressure transducer across the orifice. A first valve communicates with the high pressure side of the orifice and is connected to the high pressure side of the differential pressure transducer. A second valve provides a connection from the low pressure side of the orifice plate. A third valve connects across the transducer by connections within the manifold body between the two lines in the body. Two lines in the body are normally required to complete the necessary connections between the pipeline and the differential pressure transducer. The third valve and associated line is perpendicular to the pressure sensing lines of the body. The third valve is ordinarily included to facilitate testing, equalizing or other procedures. The third valve is opened to calibrate the differential pressure measuring instrument as an example.
The incorporation of three valves within a manifold presents three valve stems and suitable handles on stems for operation. There is a customary or desirable normal operating mode for the three valves. In the normal mode, the first and second valves are normally open while the third valve is closed. For nomenclature purposes, the first valve is the valve that connects the low side of the orifice plate to the low side of the pressure transducer. The second valve is the high side connection. As will be appreciated, the low and high side valves and their connecting lines are typically identical to one another. Confusion of the two is regrettably all too easy and improper operation often results.
In the normal operating mode, it is desirable to isolate the pressures on the two sides of the sensor or transducer. The third valve connects the two pressure lines for calibration, testing and service work on the transducer. The present apparatus is particularly adapted to interlock the valve stems to limit the sequence in which the valves can be opened and closed. It permits opening and closing in a prescribed sequence whereby the three valves are operated safely. Safety interlock systems between the three valves presently comprise suitable labels on the valves indicative of the open and closed positions. Labels will not prevent improper operation. Such labels are typically installed with the valves. The labels are successful assuming that the service personnel knows and understands precisely how the valves function and the sequence in which they must be operated. While this is desired of all service personnel, it nevertheless is not a fact. The prior art further discloses valve handle or stem protective systems including arrangements whereby the handles, stems, or both are selectively removed so that special tools (an Allen wrench as an example) are required to even operate. This interferes with ready access to the valve equipment. Moreover, it does require the use of specialty tools, and is thereby deficient in this regard.
Features of this apparatus include an interlock system whereby the three stems are interlocked with one another. They are all interlocked using circular disks of a specified diameter. The disks are selectively notched. The notches which are formed in the various disks are cut at a diameter to enable one disk to rotate while the other two disks remain locked relative to one another, being engaged at the periphery with the respective notches. The disks interlock so that only one valve can be opened. After that one valve has been opened by rotation through 90.degree., a notch on the disk of that valve stem is then rotated to enable the second disk and the second valve associated with it to rotate. When the second valve is operated, the disk which it supports is then rotated to position a notch on the second disk to enable the last valve to be operated. The three disks, in blank form, are identical for ease of manufacture. In fact, stamping and notching procedures are easily implemented as desired. Alternate manufacturing steps can be selected. They are preferably installed on a manifold having three valve stems arranged in a symetrical relationship. Specified sequences of opening and closing are thereby permitted.
This apparatus further includes a lock bar. The stems are preferably constructed of nonround stock. Ideally, hex stock is used although rectangular stock can be used. Whatever the case, the nonround stock of the stems serves as a keyed member. A lock bar is devised which is easily secured between two stems and extends past the valve body to enable a lock and chain to fasten it. When the operative condition of the manifold is altered, the lock bar is first removed, the valves are then operated, and the lock bar is thereafter reinstalled. The lock bar is keyed so that it is merely reinstalled on two stems with the same face exposed. The lock bar includes a pair of openings, keyed for fitting over a pair of valve stems such that it can be installed on both the stems to secure the stems in the two states permitted. The two states of the valves are locked by simply placing the lock bar over the stems in the only available mode of installation. If the bar fits the keyed stems, the stems are correctly rotated. If the bar will not fit, a valve has been improperly operated. This also enables the operator to know at a glance the operative condition of the multivalve manifold by virtue of color or symbol coding on the discs and exposed instrument body face. They are best color coded or otherwise painted with symbols (observed along with the lock bar) indicating the open and closed condition of the multivalve manifold.
One embodiment involves a lock bar with spaced openings keyed to fit over stems made of non-round stock. Another embodiment of the locking mechanism includes round stems drilled with holes at a common elevation. On rotation, they are aligned to enable a bicycle lock to pass through two aligned openings and fasten the stems in position. Once the stems are locked, rotation is prevented.